Circuit to control motor current or battery charging current



E. F. WEISER 3,414,795

CIRCUIT TO CONTROL MOTOR CURRENT OR BATTERY CHARGING CURRENT Dec. 3,1968 I 2 Sheets-Sheet 1 Original Filed Nov. 20, 1964 .rzuxmbu m 08 MB Mm Pa T, s E N R A E Y B \fimmzm Q Q v QUKI HIS A'ITORNEY Dec. 3, 1968 E.F. WEISER 3,414,795.

CIRCUIT IO CONTROL MOTOR CURRENT OR BATTERY CHARGING CURRENT OriginalFiled Nov. 20, 1964 2 Sheets-Sheet 2 INVENTOR. EARN EST F. \JEISER HISATTORNEY United States Patent 3,414,795 CIRCUIT TO CONTROL MOTOR CURRENTOR BATTERY CHARGING CURRENT Earnest F. Weiser, Erie, Pa., assignor toGeneral Electric Company, a corporation of New York Original applicationNov. 20, 1964, Ser. No. 412,809, new Patent No. 3,378,746. Divided andthis application Dec. 29, 1967, Ser. No. 694,738

3 Claims. (Cl. 320-9) ABSTRACT OF THE DISCLOSURE A battery-powered D-Cmotor control system in which unidirectional pulses from a choppercircuit can be for energizing a D-C motor or for charging a battery,with the circuitry used for motor control purposes also aiding incontrolling the battery charging.

Cross reference to related application This is a division of applicationSer. No. 412,809, filed on Nov. 20, 1964, now Patent No. 3,378,746.

Background of the invention This invention relates generally to acontrol circuit for a D-C motor and, more particularly, to a motorcontrol circuit for a battery powered vehicle.

In an electrically powered vehicle, as in any vehicle, it is desirableto have a motor control which produces good accelerationcharacteristics, accurate running speed control and sound brakingcapabilities. Because of their relatively small size, resistance toshock and economy, it is desirable to produce these features with staticcontrol devices. These objectives may be realized by using the solidstate motor control circuit of this invention.

Therefore, it is an obejct of this invention to provide an improvedmotor control circuit.

Another object of this invention is to provide an electrically poweredvehicle with complete solid state electronic torque control means.

Another object of this invention is to provide a motor control circuitthat yields high torque during acceleration and weakened field duringrunning at a higher speed.

Yet another object of this invention is to provide a battery poweredvehicle in which the battery may be recharged without the use ofadditional circuitry.

Briefly, in one form thereof, this invention employs electroniccircuitry to control the operations of the motor of an electricallypowered vehicle. The motor which may be a conventional D-C separatelyexcited motor, is supplied from a fixed supply, such as a battery. Motortorque is varied by converting the output of the fixed supply to a formthat can be controlled to adjust the average power supplied to the motorarmature circuit. This is achieved by using a converting means, such asa silicon controlled rectifier (SCR) chopper circuit, in series with themotor armature. The average power supplied to the motor armature isvaried by a torque control means, such as a unijunction transistoroscillator circuit, which is connected to the chopper circuit to set therate of repetition of the pulses produced by the chopper circuit.Control of the torque control means is achieved from a torque settingmeans, which is under the direct supervision of the operator. Duringoperation it is desirable to have a high torque during acceleration andless torque during running at a constant speed. These results areachieved by connecting a control means to the shunt field of the motor.The control means comprises an SCR chopper circuit and a unijunctiontransistor oscillator circuit. Setting of the control means iscontrolled by a current-measuring means, which may comprise atransistorized differential amplifier. Regenerative ice braking is alsoachieved from the current-measuring means and the control means, bycontrolling the output of the current-measuring means with a brake meansunder the supervision of the operator. Reversal of the motor isaccomplished with the aid of an interlock system to prevent to preventreversal unless the motor is at a standstill or very slow speed ofrotation. Charging of the battery is achieved by plugging into aconventional A-C supply and using the converting means and speed controlmeans to regulate the charging. Provision is made to protect the batteryfrom excessive charging current and voltage.

The novel and distinctive features of the invention are set forth in theappended claims. The invention itself, together with further objects andadvantages thereof, may be understood by reference to the followingdescription and accompanying drawings.

Brief description of drawings FIGURE 1 is a simplified block diagramillustration of the control system of this invention in its motoringmode of operation; and

FIGURE 2 is a schematic circuit diagram of a complete control system inaccordance with one embodiment of this invention.

Specification As shown in the simplified block diagram of FIGURE 1, thearmature circuit 2 of a direct current motor M is supplied controlledenergy from a fixed D-C supply through a series D-C chopper circuit.Similarly, the field winding 3 is supplied with controlled energy fromthe fixed D-C supply through a separate D-C chopper circuit. Thechopping or repetition rates of the respective D-C chopper circuitsdetermines the average power supplied to the motor armature and fieldcircuits respectively to thereby control the operation of the motor.Each of the D-C chopper circuits is provided with a control circuitwhich controls the repetition rate thereof. These control circuits aredesignated torque control circuit. and field control circuitrespectively.

The repetition rate of the D-C chopper circuit supplying the motorarmature circuit is controlled in response to the positioning of atorque setting means, such as a foot pedal controlled by the operator,for example, through the torque control circuit, which may convenientlybe a relaxation oscillator whose period is controlled by the position ofthe torque setting means. The average power supplied to the motorarmature circuit is thus controlled thereby controlling motor torque ina desired manner.

Since it is desirable to provide for a higher torque during accelerationthan during running at constant speed, the system provides for controlof the field excitation in a controlled manner so as to control theoperating characteristics of the motor. To this end, a current measuringmeans is provided for sensing the armature current. One output of thecurrent measuring means is utilized to control the field controlcircuit, which in turn controls the reptition rate of the D-C choppercircuit supplying the rfield winding 3, to regulate the field current.Another output of the current measuring means is utilized to control thetorque control circuit to assure that the armature current is limited toa predetermined maximum value.

Referring now to FIGURE 2 of the drawings, there is shown a motor Mhaving an armature circuit 2 and a shunt field Winding 3. The motor isprovided with energy from a fixed supply, such as battery 4. Since thebattery 4 is a fixed supply it is necessary to provide some means forvarying the power supplied to the motor. This is achieved by convertingthe fixed supply into a pulsating supply with a converting means, shownas a D-C chopper circuit 5. Chopper circuit 5 includes a plurality ofcontrolled rectifier devices 6, which are shown as being siliconcontrolled rectifiers (SCRs) each having an anode 7, a cathode 8 and acontrol electrode, or gate 9. The anode elements 7 of controlledrectifiers 6 are connected through a current equalizing inductor 10 tothe positive side of battery 4 and the cathode elements 8 of controlled'rectifiers 6 are connected to the lead 11. The chopper circuit alsoincludes a commutation circuit including the controlled rectifier 12having an anode 13, a cathode 14 and a gate 15. Gating pulses, toinitiate conduction in controlled rectifiers 6, are applied to the gates9 thereof through equalizing resistances 16. Power is transmitted to thecommutation circuit over the lead 11.

Equalizing inductors are well known in the art and may be convenientlyarranged to provide the desired current equalization by a suitablecombination of reactance and resistance. As illustrated, the equalizinginductor 10 comprises the three windings 17 arranged about a pair ofcommon magnetic cores 18.

The line 11 is connected to a point on a saturable core transformer 19.Transformer 19 has a pair of winding portions 20 and 21 and a saturablecore 22. Connected between winding portions 20 and 21 of transformer 19is a diode 23 and connected in series with winding portions 20 and 21and diode 23 is an SCR commutating capacitor 24. One terminal of thecapacitor 24 is connected to the negative side of the battery 4, whilethe other terminal of capacitor 24 is connected to one end of thewinding portion 21 and to the anode 13 of the SCR 12. The cathode 14 ofSCR 12 is connected between winding portion 20 and diode 23 at the pointwhere the line 11 is also connected to the transformer. A gating signalfor SCR 12 is obtained through a resistor 25 connected between the gate15 of SCR 12 and the junction of diode 23 and winding portion 21.

Since the current delivered to the armature circuit 2 of the motordepends upon the rate at which SCRs 6 are fired or gated intoconduction, it is desirable to have the firing rate determined by ameans subject to the control of an operator. This current control meansis indicated generally at 26 in the figure. The current control means 26is basically a unijunction transistor relaxation oscillator, the basicelement of which is a unijunction transistor (UJT) 27, which has anemitter 28, a base one 29 and a base two 30. The base 30 of the UJT 27is connected to the positive side of the power source through a resistor31, while the base 29 of UJT 27 is connected to the negative side of thepower source through a resistor 32. The emitter 28 of UJT 27 isconnected to the midpoint of a divider formed from a capacitor 34 and aresistor 33. Emitter 28 is also connected to one side of a capacitor 35,while the other side of the capacitor 35 is connected to the negativeside of the battery 4. Capacitor 35 is connected in series with atransistor 36, which has an emitter 37, a collector 38, and a base 39.The emitter 37 of transistor 36 is connected to the positive side of thebattery through a resistor 40. The base 39 of transistor 36 receives abias from a variable voltage device 41, which forms a voltage divideralong with resistors 42 and 43. The setting of the variable voltagedevice 41 is controlled by a current setting means 44. The currentsetting means 44 is indicated as a simple foot pedal, but may just aseasily be a remote setting means of some type. The output of theunijunction transistor oscillator is taken from between the base 29 ofthe UJT 27 and theresistor 32 and suitably amplified by application tothe base 45 of a transistor 46, which also has an emitter 47, and acollector 48. The transistor 46 is in series with a resistor 49 and awinding 50 of a transformer 51. The other side of the transformer 51 hasa winding 52 connected to the resistors 16 in the gate circuits of theSCRs 6.

The output of chopper circuit 5 is applied to the armature 2 of themotor through an inductor 53, which serves to average the current bysustaining current flow during the off time through a diode 54, which isin parallel with a resistor 55.

While the chopper circuit controls the motor torque by varying thecurrent applied to the motor armature, the current supplied to the shuntfield 3 of the motor may be varied to control the operatingcharacteristics thereof. The current supplied to field winding 3 isadjusted by control means generally indicated within the dotted lines atThe control means 56 includes a chopper circuit and unijunctiontransistor oscillator circuits similar to those discussed in connectionwith the armature supply. The chopper circuit of control means 56comprises an SCR 57, a saturable core transformer 58, and a capacitor59. The SCR 57 has an anode 60, a cathode 61, and a gate 62. The cathode61 is connected to the negative side of battery 4 and the anode isconnected to the winding of the transformer 58, dividing the windinginto portions 63 and 64.

One side of the winding portion 64 of the transformer 58 is connected tothe capacitor 59, which is shunted by a diode 65 and a resistor 66connected in series. The other side of capacitor 59 is connected to thepositive side of battery 4. One side of the winding portion 63 oftransformer 58 is arranged to be connected to capacitor 59 through theshunt field 3. The other sides of winding portion 63 and 64 are joinedtogether at the point connected to the anode 60 of the SCR 57. Connectedin parallel with the shunt field winding 3 is a parallel combination ofa diode 67 and a resistor 68. A resistor 69 is connected directly acrossthefield winding 3.

Control of the chopping rate of the chopper circuit is achieved bycontrol of the firing pulse applied to the gate 62 of SCR 57. Thiscontrol is achieved by the use of a unijunction transistor relaxationoscillator including a UJT 70, which has a base one 71, a base two 72,and an emitter 73. Power for the oscillator is obtained from the pointbetween the winding portions 63 and 64 on the transformer 58 through aresistor 74. The supply obtained through resistor 74 is regulatedconstant by a breakdown diode 75. Base 72 of the UI T 70 is connected tothe supply, obtained through the resistor 74, through a resistor 76.Similarly, base 71 of UJT 70 is connected to the negative side of thebattery through a resistor 77. The emitter 73 of UJT 70 is connected toa divider network having a parallel connection of a capacitor 78 and aresistor 79 on one side, and resistor 80 on the other side. Emitter 73is also connected to one terminal of a capacitor '81, which is chargedthrough a transistor 82. The transistor 82 has an emitter 83, acollector '84, and a base 85. The base 85 is biased from a voltagedivider network comprising resistors 86 and 87. Additional control ofthe bias condition of the transistor 82 and the chargin rate of thecapacitor 81 is obtained from another circuit on a line 88, connected toemitter 83 of transistor 82. The emitter 83 is also connected to theregulated supply through a resistor 89.

Determining the oscillating rate of the unijunction transistoroscillator, and thereby the amount of current flow in the shunt field 3,is a very important factor in obtaining the desired motor operatingcharacteristics and achieving braking of the vehicle. Setting of thefrequency of the oscillation to achieve both of these functions may berealized by the use of a current measuring circuit indicated generallyat 90. The current measuring circuit 90 is primarily a differentialamplifier formed from transistors 91 and 92. The transistor 91 has anemitter 93, a collector 94, and a base 95; while the transistor 92 hasan emitter 96, a collector 97 and a base 98. A pair of diodes 99 and 100are connected in a back-to-back arrangement between the collectors 94and 97. Collectors 94 and 97 are connected to a line 101 throughresistors 102 and 103, respectively. The line 101 is kept at a constantvoltage value by a breakdown diode 104 which is connected to thepositive side of the battery 4 through a resistor 105.

Emitters 93 and 96 of transistors 91 and 92 are joined together andconnected to the negative side of battery 4 through resistors 106, 107,and 108. The base 95 of transistor 91 is provided with a bias from avoltage divider network consisting of resistors 109 and 110. Base 98 oftransistor 92 is biased from a voltage divider network comprisingvariable voltage device 111 and fixed resistances 112 and 113.

Setting of the frequency of oscillation of the unijunction transistorrelaxation oscillator circuit is achieved by taking an output signalfrom the collector 94 of transistor 91 and applying it to the UJToscillator circuit in control means 56 through a voltage responsivedevice. The voltage responsive device in this case is a transistor 114having an emitter 115, a collector 116, and a base 117. The emitter 115is connected to the negative side of the battery 4 through a resistor118 and the resistor 108. The collector 116 of transistor 114 isconnected over line 88 to control means 56. The output of collector 94of transistor 91 is determined either by the mag nitude of the armaturecurrent causing a voltage drop across resistor 108, or by the brakemeans 119. As in the case of accelerator 44, the brake means 1.19 isshown as a foot pedal, but may just as easily be a remote brakingcontrol.

Another output of the difierential amplifier may be taken from a pointbetween the diodes 99 and 100. This output is applied to a breakdowndiode 120. In order to break down the diode 120 when the armaturecurrent is large, the output of the differential amplifier reaches andexceeds the breakdown voltage of the diode 120. The breakdown diode 120is connected to base 121 of transistor 122, which has an emitter 123 anda collector 124. The collector 124 is connected to emitter 37 oftransistor 36, while emitter 123 is connected to the negative side ofbattery 4. The bias supplied to base 121 of transistor r122 uponbreakdown of the diode 120 is such as to set a minimum value upon thetime of charging capacitor 35 so that the motor current is limited to amaximum value.

As it will be necessary to recharge the battery 4 from time to time,provision has been made to use converting means and control circuit 26to adjust the charging rate. The use of circuits 5 and 26 to controlbattery charging is made possible by the switch elements 125, 126, and127. The switch elements 125, and 126, upon actuation, serve to placethe battery 4 in the circuit where the motor was originally located.Thus, the battery 4 is no longer the power supply but is the load in thecircuit. Switch element 127 serves to disconnect line 128 which servesas a regenerative braking path through rectifier 129 during braking ofthe running motor.

Power for charging the battery is obtained from a conventional AC source130. The output of source 130 is full wave rectified by the rectifier129 and applied to the battery line 131. Rectifier 129 includes diodes132 through i135 placed in a full wave bridge arrangement. A capacitor136 and a resistor 137 are connected between the input terminals of thebridge, and resistors 138 and 139 are located in the arms of the bridgeoccupied by diodes 134 and 135, respectively. Resistors 138 and 139 areoperative to equalize current during braking.

The charging current for battery 4 is controlled in the same manner asthe armature current of the motor during running condition, except thata lower maximum current value is set by placing resistor 107 in thecircuit by means of the switch element 127. A maximum charging voltageis also desired and this maximum value is set by a resistor 140 and adiode 141, which serve to break down the breakdown diode 120 upon theoccurrence of excessive charging voltage, in the same manner thatbreakdown diode 120 is broken down upon the occurrence of an excessivearmature current or charging current. Fluctuations in the chargingcurrent are reduced by the use of a capacitor 142 connected acrossbattery 4.

Since it is desired to drive the vehicle in a reverse direction as wellas in a forward direction, it is necessary to provide some means forreversing the direction of rotation of the motor. To this end a switch143 is provided. By placing the switch 143 in either position 144 or145, relay coil 146 or relay coil 147 is energized. The relay coil 146is energized through a diode 148 and a resistor 149, while relay coil147 is energized through a diode 150 and a resistor 151. A diode 152blocks the signal obtained through the diode 148 or the diode 150 duringrunning of the motor, but provides a path for breakdown of the diode 104during the charging operation. The relay coil 146 controls relaycontacting elements 153 and 154, while relay coil 147 controls relaycontacting elements 155 and 156. A diode 157 is connected between themotor armature and contacting elements 153 and 154 to aid in theproduction of an interlock system which prevents motor reversal exceptat stand-still or low speeds.

The operation of the control system will now be described.

During running When switches 125, 126, and 127 are in the positionsshown in the drawing the control system is in the motor run position.With the switches in this position the positive side of the battery 4 isconnected to the anodes 7 of SCRs 6 through switch 125. The gating ofSCRs 6 is controlled by the control circuit 26. A supply is obtained forthis circuit from the line v101 which is held at a constant voltagevalue by the breakdown diode 104. The frequency of oscillation of theunijunction transistor oscillator in control means 26 depends upon therate of charging of capacitor 35. Determination of the charging rate ofcapacitor 35 is achieved by transistor 36, which is controlled by thevariable voltage device 41. For instance, if torque setting means 44 isactivated to position the variable voltage device 41 to increase thebias on base 39 of transistor 36, the conduction of current throughtransistor 36 will be increased and the charging rate of capacitor 35will be increased. When capacitor 35 reaches a suflicient high value ofcharge the voltage on the emitter 28 of UJT 27 will be suflicient topromote breakdown of the UJT and permit current flow through resistor32. This in turn produces a signal upon the base 45 of transistor 46 toproduce conduction through this transistor and apply a gating voltage toSCRs 6 through transformer 51.

When SCRs 6 are fired the positive output of battery 4 is applied to thepoint between winding portion 20 and diode 23. This potential produces acurrent through winding portion 20 and the motor armature circuit 2, anda second current through diode 23 and winding portion 21 to chargecapacitor 24. The current through winding portion 21 quickly causes anegative saturation of core 22 and capacitor 24 is charged to the supplyvoltage. At this time the current through winding portion 20 begins toincrease and the core is driven towards positive saturation. During thisperiod a transformer action results between winding portions 20 and 21and the capacitor is charged to a voltage greater than that produced bythe power supply. When the voltage drop across resistor 25 exceeds apredetermined value because of the transformer action, a voltage ofsufiicient magnitude is applied to gate 15 of SCR 12 to fire SCR 12 anddischarge capacitor 24, to thereby commutate or turn-off SCRs 6 byapplying a reverse bias thereto. Since the pulses formed in this mannerand applied to armature 2 have a uniform duration, the average powersupplied to the motor armature depends upon the repetition rate of thepulses. Therefore, torque control circuit 26 and chopper circuit 5control the average power applied to the armature circuit of the motoras a direct result of the control exerted by torque setting means 44.

As explained previously, the inductor 53 sustains current during the oiltime of the pulses so that the energy applied to the armature of themotor is averaged.

Acceleration control The armature current through the motor is detectedby the current-measuring circuit 90 and used to control the current inthe shunt field winding 3. Detection of the armature current magnitudeand production of a control Signal is achieved by the use of thedifferential amplifier comprising transistors 91 and 92 and the resistor108. As the armature current increases, the voltage drop across resistor108 increases and since the voltage on line 101 is fixed at a constantvalue by breakdown diode 104, the voltage at the point between resistors.109 and 110 also increases. This increase in voltage at the pointbetween resistors 109 and 110 increases the forward bias on transistor91 and causes it to conduct more heavily. This increased current alsoincreases the total current through resistors 106 and 107 and thusincreases the potential on emitters 93 and 96, which tends to decreasethe current through transistors 91 and 92. The decrease in current thendecreases the voltage on emitters 93 and 96 which in turn promotesanother increase in current. However, after a short period of time abalanced condition is reached in which a greater amount of current flowsthrough transistor 91 than through transistor 92. Since the current flowthrough transistor'91 is greater than the current flow throughtransistor 92 the voltage drop across resistor 102 is greater than thevoltage drop across resistor 103, so that the potential on collector 94is at a lower value than the potential on collector 97.

The potential at collector 94 of transistor 91 is applied to base .117of transistor 114 which acts as a voltage responsive device in responseto the change in output of the differential amplifier. This decrease inpotential on the base of the transistor 114 reduces its forward bias andcauses a reduction in the current flow through the transistor, or anincrease in the resistance of transistor 114. This reduced current flow,or increased resistance, is used to control a unijunction transistoroscillator in control means 56. This UJT oscillator is essentially thesame as the UJT oscillator described in the speed control circuit 26.

In the UJT oscillator located in control means 56, the capacitor 81corresponds to capacitor 35 in torque control means 26, and transistor82 corresponds to transistor 36. However, transistor 114 is connected inparallel with transistor 82 and capacitor 81. As the current flowthrough transistor 114 decreases and the resistance of transistor 114increases, the current flow through transistor 82 increases. This is sobecause the voltage on line 88 remains the same as the resistance oftransistor 114 increases, but the decreased current flow throughtransistor 114 means that the current flow through transistor 82 mustincrease to maintain the same voltage drop across resistor 89. Theincreased current flow through transistor 82 causes capacitor 81 tocharge at a greater rate so that unijunction transistor 70 is fired morefrequently and the rate of oscillation is increased. The output of theUJT oscillator is applied to a chopper circuit, similar to the choppercircuit described above, to increase the chopping rate, or repetition,rate of current pulses. This increase in the repetition rate of currentpulses increases the average current through shunt field 3 and therebyincreases the flux in the motor.

It should be noted that as the armature current decreases the current inshunt field 3 will also be decreased so that at a constant running speedthe field current will be only that necessary.

Since the operation of the chopper circuit in the control means 56 issomewhat different from that shown in the chopper circuit 5, theoperation of this circuit will now be briefly described. Upon firing ofSCR 57 by the output of the unijunction transistor oscillator applied togate 62 of the SCR 57, conduction occurs through winding portions 63 and64 of the saturable core transformer 58. The current flow throughportion 63 is from the positive side of the power supply through switch154 or 156, depending upon whether the motor is in the forward orreverse operating condition, shunt field 3, winding portion 63 and SCR57 to the negative side of the power supply. Similarly, the currentthrough winding portion 64 is from capacitor 59 to the negative side ofthe power supply. Since the ampere turns of portion 64 is large duringthis charging period the core is driven to negative saturation to chargethe capacitor to the full value of the power supply upon saturation ofthe core of transformer 58. After this negative saturation of the core,the current through the load and winding portion 63 increases and startsdriving the core in the positive saturation direction, meanwhileincreasing the voltage across capacitor 59 to above the potential of thepower supply by transformer action. This increased current in portion 63causes core saturation in the forward direction. Upon saturation of thecore in the forward direction capacitor 59 discharges and turns off orresets SCR 57. Due to the high potential formed across capacitor 59, thedischarge through winding portions 63 and 64, and the field winding 3 isquite large and would normally produce a high positive voltage on theside of capacitor 59 which is connected to winding portion 64. However,diode 65 and resistor 66 have been added to prevent this occurrence sothat upon reset of the circuit, when the voltage at this point exceedsthe voltage of the power supply, conduction will occur through diode 65to prevent overshoot of the capacitor voltage and the resultingexcessive reset of the saturable core transformer 58.

Braking The operation just described for producing desirableacceleration characteristics is the same that occurs during continuouslyvariable regenerative braking, since an increase in the current in field3 increases the flux in the motor, thereby increasing the counter EMFabove the battery voltage and producing regenerative charging of battery4. The only difference in operation is that transistor 92 of thedifferential amplifier is that which produces the initial action toprovide an output signal. For instance, if braking is desired thevariable voltage device 111 is set to a lower potential value by thebraking means 119. This reduces the bias on base 98 of transistor 92 toreduce the current flow through transistor 92 and thereby reduce thevoltage drop across resistor 103, while increasing the voltage dropacross resistor 102 to produce the same increase in signal that isrealized upon the production of a large armature current. This actionproduces a continuously variable braking, rather than the step-by-stepbraking achieved with prior art braking devices.

Charging During the charging operation switches 125, 126, and 127 arethrown to the opposite postions from that shown in the drawing. By thisswitch arrangement the battery replaces the motor in the circuit as theload. Power is now applied to the circuit through line 131 from therectifier 129. The operation of chopper circuit 5 and speed controlcircuit 26 is the same as that described above for running of the motor.Switch 127 removes the regenerative braking path and adds resistor 107to resistor 108 in the current return path. This additional resistormeans that the torque control circuit 26 will have a lower maximumfrequency.

The current limiting feature in both this phase and the motor runningphase is a result of the differential amplifier, comprising transistors91 and 92, the operation of which has been previously described. When alarge current produces the differential amplifier action described abovesuch that, for example, the voltage drop across resistor 102 is greaterthan the voltage drop across resistor 103, the difference in thevoltages produces an output voltage at the point between diodes 99 and100. This voltage will be that produced in the circuit with the lowercurrent flow, as in this example it would be the voltage on collector97, since diode 99 will be back biased. This voltage is then applied tothe breakdown diode and it the armature 9 or charging current is greatenough the voltage drop across resistor 103 will be so small that thediode 120 will be broken down. Breakdown of diode 120 biases transistor122 to a point that limits the current flow through transistor 36 andtherefore limits the charging rate of capacitor 35.

During the charging operation a voltage limiting effect is also obtainedby placing resistor 140 across the battery. The voltage obtained fromresistor 140 is applied to breakdown diode 120 through diode 141 and ifthe voltage across the battery exceeds a specified value diode 120 willbe broken down and a maximum unijunction transistor oscillator frequencywill be set, as in the current limiting phase described above.

Motor reversal Motor reversal is achieved by switch 143. If switch 143is placed in position 144 the relay coil 146 will be energized throughresistor 149. Energization of relay coil 146 results in the closing ofrelay contacting elements 153 and 154. By moving switch 143 to position145, relay coil 147 will be energized and close relay contactingelements 155 and 156, if the motor is at stand-still or a low speed.

Since it is desirable to prevent motor reversal if the motor speed ismuch above stand-still, the diode 157 is connected from the motorarmature to the contact 153. If the motor speed is then at a valuesufficient to produce a sizable back EMF, the relay coil 146 will stillbe energized even though switch 143 is thrown to posiiton 145. Amechanical interlock or bias arrangement (not shown) is provided betweenthe contacting elements 153 and 155 so that as long as the contactingelement 153 is held in its closed position the contacting element 155cannot be closed. The same is true for the contacting element 156. Thus,motor reversal is prevented unless the motor is at stand-still or a verylow speed.

Although the invention has been described with respect to certainspecific embodiments, it will be appreciated that modifications andchanges maybe made by those skilled in the art without departing fromthe basic teachings of the invention. Therefore, it is desired not tolimit the following claims to the specific embodiments shown, but tocover all modifications and changes within the spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a battery-powered D-C motor circuit, a control system comprising:means for converting a unidirectional signal into a series ofunidirectional pulses; means for selectively applying the unidirectionalpulses to motor or to a battery; torque control means for setting therepetition rate of the unidirectional pulses; current measuring meansincluding dilferential amplifier means for selectively connecting saidcurrent measuring means to the motor or to the battery to detect themagnitude of the motor armature current or the battery charging current;a breakdown voltage device connected between said differential amplifierand said torque control means to limit the repetition rate of theunidirectional pulses when the magnitude of the current exceeds apredetermined value; and means for selectively obtaining theunidirectional signal from the battery to power the motor or from anexternal source to charge the battery.

2. A control system as recited in claim 1 wherein said means forconverting a unidirectional signal into a series of unidirectionalpulses comprises a controlled rectifier chopper circuit; said torquecontrol means comprises a relaxation oscillator; and said means forselectively ob taining said unidirectional signal comprises a switchingcircuit.

3. A control system as recited in claim 1 and further comprising: meansto limit the magnitude of the voltage across the battery during chargingof the battery, said last-named means being connected to said breakdowndevice to limit the frequency of repetition of said unidirectionalpulses when a predetermined voltage magnitude is exceeded.

References Cited UNITED STATES PATENTS 3,207,966 9/1965 Parkinson 3205 X3,305,760 2/1967 Davis et al 321- 3,316,417 4/1967 Tolmie 318l39 JOHN F.COUCH, Primary Examiner. STANLEY WEINBERG, Assistant Examiner.

